WASHINGTON — Top career officials in the Internal Revenue Service withheld information from Congress for months about the tax agency's targeting of conservative organizations for extra scrutiny, according to documents released Monday as a controversy involving alleged political bias in tax enforcement gathered strength.

Members of Congress called for firing the agency's acting commissioner, one of the senior officials involved, and President Obama said he would "not tolerate" any such abuse of power by the IRS.

"If you've got the IRS operating in anything less than a neutral and nonpartisan way, then that is outrageous; it's contrary to our traditions. And people have to be held accountable, and it's got to be fixed," Obama said at a White House news conference, noting that the IRS' practices are under investigation. "We'll wait and see what exactly all the details and the facts are. But I've got no patience with it. I will not tolerate it. And we will make sure that we find out exactly what happened on this."

House Ways and Means Committee Chairman Dave Camp (R-Mich.) announced a hearing Friday. "News that the agency admits it targeted American taxpayers based on politics is both astounding and appalling," he said. "It is almost inconceivable to imagine that top officials at the IRS knew conservative groups were being targeted but chose to willfully mislead the committee's investigation into this practice."

Despite calls for firings, neither the president nor members of Congress have legal authority to fire any IRS officials other than the commissioner and general counsel, who are the agency's two political appointees. Neither of those jobs is currently filled.

Top officials at the IRS didn't reveal the improper targeting until Friday, when it acknowledged mistakes it said had been made by its Cincinnati office, the main office handling tax-exempt entities — although members of Congress started asking questions about the agency's handling of tea party organizations as early as 2011.

On Monday, Jay Sekulow, a lawyer representing 27 tea party groups, said IRS queries came not only from Cincinnati but from offices in Washington, D.C., and Laguna Niguel and El Monte, Calif.

Sekulow, a former lawyer for the IRS chief counsel's office, said the groups would continue to press for answers on who was guiding the review of tea party groups. "Agents can't do that on their own," he said.

Some groups were sent detailed questionnaires that asked about their relationships with candidates or public officials, details of their fundraising pitches and their lists of donors.

The controversy centers on "social welfare" organizations set up under section 501(c)4 of the tax code, which can participate in elections as long as politics is not their primary purpose. Unlike political committees, such groups are not required to disclose their donors. Social welfare groups had a limited role in campaigns until 2010, when the Supreme Court ruled in the Citizens United case that corporations could spend unlimited sums on elections — a decision that also unleashed a flood of spending by the nonprofit groups.

The IRS staff has the job of determining which groups qualify for tax-exempt status. Lois Lerner, the IRS director of exempt organizations, said the disputed actions were devised as shortcuts by workers dealing with a flood of applications from groups seeking to become tax-exempt social welfare organizations.

The agency has acknowledged that employees in Cincinnati, in reviewing applications for nonprofit status, inappropriately singled out conservative organizations whose applications included the words "tea party" or "patriots" for closer examination.

But at least two top agency officials repeatedly assured members of Congress in 2012 that the IRS was processing applications in a smooth and consistent manner, even though they knew of the problems.

Steven T. Miller, a 20-year veteran of the agency who is the acting IRS commissioner, first learned on May 3, 2012, that the agency had inappropriately singled out groups by name, the IRS told the Los Angeles Times. A month later, Miller made no mention of the matter in a letter to Congress about the issue.

In a June 15, 2012, letter to the chairman of a key House oversight subcommittee, Miller wrote that after an increase in applications for tax-exempt status in 2010, the agency "took steps to coordinate the handling of the cases to ensure consistency."

Miller, then deputy IRS commissioner, noted that some applications had lingered "for a longer time than expected," according to the letter obtained by The Times. And he made an allusion to some internal problems, writing that, in early 2012, "issues with respect to these cases were brought to the attention" of top officials who "ensured more timely and consistent handling of the cases."